The present invention relates to a hydraulic pump circuit for excavators, in particular, as well as other machines that have hydraulic systems for operating components and for ground drive. The hydraulic circuit includes three pumps, one of which is normally used for hydraulic power for auxiliary attachments, and which can be coupled to the drive circuit for propulsion, to provide an increase in speed of travel of the machine at desired times. Additionally, the hydraulic circuit has all three pumps plumbed into a single relief valve to simplify the overall operation.
U.S. Pat. No. 6,018,895 shows a valve stack for a mini-excavator that has multiple hydraulic pumps, to provide flow for various purposes. In patent ""895, the valve block provides a series connection between certain of the operating cylinders and the vehicle drive. The machine illustrated in patent ""895 is the type of machine with which the present hydraulic circuit operates.
Various types of operations are carried out with the hydraulic system of an excavator, including powering the drive motors for driving tracks. Excavators have a boom and arm that are operated with a hydraulic cylinders to pivot the boom and arm. The boom is capable of being swung about a generally vertical axis. The arm is pivoted to the boom and a bucket is mounted on the arm. Both the arm and bucket are operated with hydraulic cylinders. A blade can be used, and raised and lowered by actuating a hydraulic cylinder. The blade can be considered as an auxiliary component, and in addition there can be auxiliary machines such as mowers or the like that might be held at the outer end of the arm and driven with a hydraulic motor.
The cab of an excavator is generally capable of rotating about an upright axis through the operation of a hydraulic motor as well. Thus, it can be seen that the modern excavator requires substantial hydraulic power, and efficient use of this power can be made with appropriate hydraulic circuits.
The present invention relates to efficiently operating a multiple hydraulic pump system that is used for powering various hydraulic actuators, and also for providing a drive power for motors used to propel the machine on which the hydraulic system is used. There are a plurality of motors, as disclosed three, and efficient use of the output of these motors is desired in order to obtain high operating efficiency of the machine.
The present invention includes a unique valve block for controlling the flows from three pumps, including a single relief valve for providing the high pressure relief for all three of the motors. Additionally, while two of the pumps are generally used for operating the excavating boom, the arm, boom swing, and buckets, and since these components are not normally operated during travel, the right and left hand travel or drive motors are also normally powered by first and second pumps, respectively.
The third pump is used for controlling the xe2x80x9cslewxe2x80x9d motor for or cab and mounting frame rotation for the blade that is normally used for backfilling, and also for auxiliary hydraulic components.
The operations of the various actuators for boom swing, arm, bucket, and boom pivot are conventional, as is the operation of the slew motor, the blade and the auxiliary devices. The controls are standard valves, and can be operated with conventional joy sticks or similar controls. The motors for driving the ground drive tracks of the excavator are normally operated with levers that are moved back and forth by hand to drive the respective side motors either in forward or reverse.
In addition to having a single relief valve coupled to provide high pressure relief for all three pumps, to thereby eliminate the need for individual relief valves, one of the pumps, which is normally used for auxiliary operations and also for the slew motor and blade, is made to so that it will provide pressure to these functions, including auxiliary devices, even when the travel motors are working and the excavator is moving. However, by operation of a valve at a selected time, the operator can add the volume of flow of the third pump into the circuit for driving the track drive motors and thereby increasing the speed of the machine as it moves over the ground.
The pump that provides the output that can be added to the drive motors also is arranged in the system so that it can be used for running auxiliary operations at the same time the ground drive motors for the excavator are being operated by the other pumps. In other words, the third pump acts independently to power auxiliary equipment and does not require the vehicle to be standing still. This is helpful if operations such as mowing along a strip is to be performed while the excavator is moving from one job to another. There is no need to stop and swing the arm to mow the ground.
The valve block for the motor outputs thus provides various functions that simplifies the component arrangement, while enhancing operation and reducing costs.